Chelating Agents & Treatment of Poisoning 399
Prevention of Poison Absorption
The aim is to reduce the absorption of
poison.
- Gastric lavage may be useful for six
hours after ingestion of poison. The
lavage should be done as early as
possible but only if vital functions are
adequate. - It is inappropriate to employ gastric
lavage unless the lungs can be
protected, either by virtue of patient
having an adequate cough reflex or by
means of a cuffed endotracheal tube. - Gastric lavage is contraindicated if
corrosive or caustic substances have
been taken, because oesophageal and
gastric erosion and perforation may
occur. - Activated charcoal is probably more
effective than either emesis or lavage.
Accelerating Poison Elimination
Alkalinisation of urine (alkaline
diuresis) is effective for salicylates and
phenoxyacetate herbicides.
Repeated dose of activated charcoal
administered by oral route have been
shown to enhance the non-renal elimi-
nation of carbamazepine, salicylates,
phenobarbitone, phenytoin, digoxin,
theophylline and meprobamate. In se-
vere cases activated charcoal is to be ad-
ministered via a nasogastric tube.
Haemoperfusion, using a cartridge
containing charcoal or an uncharged resin
is effective in enhancing drug excretion in
few selected cases of poisoning e.g.
theophylline, barbiturates, non-barbiturate
hypnotics, etc. (Also see Section I for the
management of poisoning).
Frequent administration of activated
charcoal is effective for the following
substances:
- Substances which form masses: Aspirin,
iron, lithium, enteric-coated tablets,
meprobamate. - Substance which remain in the stomach
for a long time: Barbital, aspirin, iron,
alcohol, cholinergic blockers, narcotic
drugs, phenytoin, antidepressants. - Substances which have a long half-life
when present in large amounts: Theo-
phylline, aspirin, alcohol, phenytoin,
chloral hydrate, acetaminophen. - Substances which have active metabolites:
Benzodiazepines, chloral hydrate,
acetaminophen, antidepressants,
procainamide. - Substances whose poisonous metabolites are
eliminated slowly: Ethylene glycol, metha-
nol, primidone, isopropyl alcohol, car-
bon tetrachloride, levothyroxine. - Substances which are reabsorbed from the
urinary tubules in a pH dependent manner:
Phenobarbital, aspirin, amphetamine. - Substances with persistent tissue accumu-
lation: Iron, lithium. - Substances which enter the enterohepatic
circulation: Carbamazepine, digoxin,
phenobarbital.
The specific antidotes for various
poisons are listed in table 11.1.1
ORGANOPHOSPHORUS POISONING
These compounds are mainly used as
agricultural and household insecticides.
The poisoning may be occupational (for
those who are involved professionally with
these agents), accidental (accidental con-
sumption) or suicidal due to intentional
ingestion of these compounds.